<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8">
        <title>className</title>

    </head>
    <body>
        <em>倾斜</em>
        <div id="box" class="mystyle">
            <span>Hello</span>
            <p>World</p>
        </div>
        <a href="#">a是div的兄弟节点</a>
        <script type="text/javascript" src="firstElementChild.js"></script>
    </body>
</html>